Spinal plates may be introduced from the anterior to stabilize the cervical spine and maintain in position or secure a bone graft which fills the spaces left by the extraction of at least one vertebral disc and, possibly, part of a contiguous cervical vertebra.
The bone anchorage screws used for fixing this type of plate in position are either unicortical, and therefore short, since they pass through only the anterior cortical of the vertebra, or bicortical, and therefore long, since they extend through the anterior cortical and the posterior cortical. The short unicortical screws utilize a locking element when there is a possibility the screws may back-out. On the other hand, the long bicortical screws, while less likely to unscrew, have other limitations making them less desirable in certain situations.
In practice, the locking element employed up to the present time for unicortical screws is an additional screw which is positioned between two bone anchorage screws and whose head overlaps the heads of these two screws. While there are thin cervical plates without a locking element, the addition of an existing locking element to a given plate design typically results in an increase in plate size, such as the plate's thickness. These additions may also result in a greater plate width than is desirable. Thus, the general desire to further decrease the size of surgical implants indicates a need for new plate and/or locking element arrangements.